Time-limit device



Sept. 11, 1923. 11,,467fi5il c. D. AINSWORTH TIME LIMIT DEVICE Filed Jan. 4, 1918 gww m Patented Sept. ll, 1923.

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CHESTER D. AINSWORTH, 0F WOLLASTON, MASSACHUSETTS, ASSIGNOB, IO SEARS B.

GONDIT, 33., OF BOSTON, HIASSAGHUSETTS. i

TIME-LIMIT DEVICE.

Application filed January 4, 1918. Serial No. 210,392.

To all whom it may concern:

Be it known that I, C'HEsTEn D. Ains- WORTH, a citizen of the United States, and a resident of VVollaston, county of Norfolk, and State of Massachusetts, have invented an Improvement in Time-Limit Devices, of which the following is aspecification.

My invention relates to overload or trip coils associated with an oil switch and has especial reference to matter shown and described but not claimed in my co-pending application, Serial No. 2 17 ,932, filed August 2. 1918.

The trip coils associated with such a switch are usually provided with means whereby the operation of said coils to trip the switch is delayed for a certain interval of time. The time limit means usually provided consists of a dash pot or cylinder filled with oil secured to the coil in which is slidably disposed a piston, which is connected with, and its movements controlled by, a movable. element or core of the trip coil or solenoid. Such time limit devices must be quite accurately constructed to be reliable in operation, and are therefore correspondingly' expensive of construction.

An object of my invention is in the design of a time limit means for-a trip coil which is inexpensive in construction, and at the same time simple, positive and reliable in operation.

The trip coils associated with an oil switch are commonly enclosed within the switch casing, and are either entirely or partially immersed in the oil contained in said casing. It is a feature of my invention to employ the oil within the casing, and which is used for insulating purposes, to operate in conjunction with the piston and cylinder of the time limit means of the overload or trip coils to retard the operation of the coil instead of providing a separate supply of oil for each trip coil.

The means whereby I accomplish the objects of my invention is in the utilization of the central hollow tube upon which the solenoid is wound, and in which the movable element or core thereof is disposed, for the cylinder of the dash pot, and I provide the core of the trip coil with a piston arranged within said hollow tube or cylinder. Said disposition of the time limit device results in a simplification of parts, and the construction is such that a minimum of accuracy is necessary, whereby the'cost of production is correspondingly reduced.

Fig. 1 is a sectional view of the oil receptacle of the switch casing, showing the normal posit-ion of the trip coil and time limit means.

Fig. 2 is a sectional view of the trip coil in its return to normal position from an operative position.

Fig. 3 is a detail partly in section of the core and piston.

Fig. 4 is a sectional view of the piston.

Fig. 5 is a plan view of the piston.

Fig. 6 is a section along lines 6-6 of Fig. 3. i,

As here shown, the solenoid comprises the tube 10, which forms the cylinder of the time limit device. A plug 11 of magnetic material is secured in the upper end of said tube 10 by the rivet 12. A screw 13, arranged in said plug, forms means whereby the trip coil may be secured to the base or frame 14. of the switch, where it may depend into the oil contained in the receptacle 15. A winding 16 is arranged upon the tube 10 between suitable heads 17.

The movable element or core of the trip coil comprises the cylindrical rod 18, which is of smaller diameter than the tube 10 and is arranged therein. Said core 18 is provided at its lower end with a striking disc 19 secured thereto by a screw 20. Said core 18 is in normal engagement with a rod of the trip coil adjusting means 21, whereby the calibration may be adjusted for a predetermined current flow. The core 18 is sufficiently smaller in diameter than the tube 10, so that a cap 22 may be secured on the end thereof in a manner to be more 'fully described. The diameter of the core 18 is ap preciably smaller than the internal diameter of the cap 22 to provide a clearance space 25 therebetween for a purpose hereinafter to be described.

Said cap 22 is arranged to be a sliding fit within the cylinder or tube 10, and forms the piston of the time limit means. The clearance between the piston 22 and cylinder 10 is such that the flow of oil therebetween, upon the effective energization of the coil, is at such a rate as to insure the proper slow upward movement of the core.

The piston 22 is formed iwithitwo diametrically opposed ears 23, which are adapted to be bent within suitable recesses 24 in the core 18, whereby the piston is secured to the core against removal therefrom. Said recesses 24- are suiiiciently large in diameter in compari son with the width of the ears 23, whereby a restricted relative motion may take place between the piston and core. The top wall of the piston is provided with an opening 26 therethrough, through which oil may flow upon certain conditions of operation of the device.

The solenoids are arranged to be immersed in the oil within the receptacle 15 of the switch to a depth suflicient to fill, or substantially fill, the space between the piston 22 and the plug 11, disposed in the top of the cylinder or tube 10.

In the normal and insufliciently energized. condition of the solenoid, the core 18, with the attached piston 22, is disposed in the lower part of the tube 10 in contact with the adjusting member 21. In such position of the core and piston, the flat end wall of the piston 22is in contact with the cor-- responding fiat end 27 of the core 18, which thereby forms a valve preventing passage of oil from the cylinder 10 through the opening 26, and the clearance space 25, to the main body of oilcontained in receptacle. The oil above the piston being thus confined, and upon such sufiicient energization of the core 18 as to cause said coreto move upward within the solenoid, tends to resist this upward movement and, due to the forces exerted uponthe confined body of oil, oil is forced between the piston and walls of the cylinder into the main body of oil in the receptacle 15. The rate of upward movement is thereby determined by the rate of oil leakage between the piston 22 and the cylinder 10, which rate is predetermined by the clearance between said pis ton and cylinder. The restricted escape of oil from the cylinder, therefore, delays the effective operation of the trip coil.

When the core 18 of the solenoid and its attached piston 22 has reached the top of its stroke and has operated to trip the switch, and the coils thereby become deenergized, the core 10, being no longer attracted in elevated position, tends to fall by gravity, and moves downward relative to the piston 22, by an amount determined by the clearance between the cars 23 of the piston and the recesses 24 in the core; the piston meanwhile being maintained against movement with the core because of the viscosity of the oil between the walls of the piston and the cylinder 10.

Due to the relative movement between the core and the piston, the end wall of the piston 22 is consquently moved from engagement with the end 27 of the core 18 "and a free passage for the circulation of oil from above the piston and the main body of oil surrounding the solenoids is possible, through the opening or port 26 in the end wall of said piston and the clearance space 25.

The weight of the core 18, acting upon the piston 22, serves to move said piston clownward, and there being substantially no restriction to the flow oi oil to the space between the piston and the end of the cylinder 10 i'ormedby the plug 11, said core and piston may move rapidly downward to the original unenergized position, where it is again in condition for effective operation.

The rapid return of the-core l0 and attached cylinder forms a desirable feature of the device, in that it prevents the obiectionable creeping of the movable element of the trip coilcommon to certain types of time limit devices.

1. A dash pot including a tube, a core operably disposed within the tube having recesses in its side wall, and a piston hating a top wall and a side wall movably arranged in said tube for restricted fluid leakage pi st its side wall, said piston side wall having integrally formed ears extended inwardly from its lower edge and received in the recesses in said core.

2. A dash pot structure comprising a tube, a rod movable therein, a piston having an apertured end wall received in said tube over the end of said rod, the end of said rod and the end wall of said piston cooperating to form a valve, said rod having a recess in its side wall, and said piston having an ear integrally formed with its side .Wall loosely received in said recess whereby to admit of restricted relativel movement between said rod and piston to open and close the valve.

3. A dash ,pot structure having a tube comprising a cylinder, a piston movably disposed within said tube having an internal recess therein and an aperture through its top wall in communication with said internal recess, said piston arranged for restricted fluid leakage between its side wall and said tube, and an actuating member comprising a rod having an end-portion substantially smaller than and disposed within said internal recess in said piston and loosely connected with said piston and arranged for free passage of fluid between itandsaid piston, said rod arranged to be moved to seal the aperture in said piston and thereafter move said piston within said tube with retarded movement.

In testimony whereof, I have signed my name to this specification in the presence of. two subscribing; witnesses.

CHESTER D. AINSlVORTH.

Witnesses:

GORDON CAMERON, T. T. Grnmvwoon. 

